Niacin is different from other vitamins because nicotinamide is biosynthesized from tryptophan. We have studied tryptophan-nicotinamide metabolism to elucidate the physiological importance of this tryptophan-nicotinamide conversion pathway for maintenance of niacin nutritional status in rats and humans. Human studies revealed that 1 mg of nicotinamide was converted from a tryptophan intake of 67 mg, and that the conversion ratio of tryptophan to nicotinamide was enhanced from mid to late pregnancy in a time-dependent manner. Animal experiments showed that the supply of nicotinamide from tryptophan was able to maintain a sufficient niacin nutritional status without niacin intake, and that the liver, but not the kidney, played a critical role in the synthesis of nicotinamide from tryptophan. Phthalate esters dramatically increased the tryptophan-nicotinamide conversion via inhibition of aminomuconate semialdehyde decarboxylase, the key enzyme in the tryptophan-nicotinamide conversion pathway.

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The purpose of this study was to clarify the effects of nutrients on the gonadal development of male rats kept under constant darkness as a model of disturbed daily rhythm. In the present study, the effects of water- and fat- soluble vitamins, and their interactions, were examined. This study was based on three-way ANOVA. The three factors were lighting conditions, water-soluble vitamins, and fat-soluble vitamins. The levels of dietary water- and fat-soluble vitamins were low, normal, or high: 1/3.3 of normal (AIN-93G diet) content, normal content, or three times the normal content, respectively. The level of protein was low, 9% casein, and other components were the same as those of the AIN-93G diet. Four-week-old Fischer 344 rats were kept under constant darkness or normal lighting (12-h light/dark cycle) for 4 weeks, and then the gonadal weights and serum testosterone concentrations were evaluated. Lighting conditions, and the interaction between lighting conditions and water- and fat- soluble vitamins, were observed to affect testis weight. Among the constant darkness groups, the highest testis weight was observed under a high water- and low fat-soluble vitamin diet, and the lowest weight was observed under a normal water- and high fat-soluble vitamin diet. On the other hand, among the normal lighting groups, the highest testis weight was observed under a normal water- and fat-soluble vitamin diet. Lighting conditions and water- and fat-soluble vitamins had no effect on serum testosterone concentration. These results suggest that the requirement of water-soluble and fat-soluble vitamins for gonadal development increases and decreases, respectively, when rats are kept under constant darkness as a model of disturbed daily rhythm, in comparison with normal lighting conditions.

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We conducted a cross-sectional study to examine the relationship between milk and dairy product consumption by Japanese adults and the development of metabolic syndrome. The subjects were employees working for four groups of milk and dairy product manufacturing companies and their families (aged 20-69 yr). We sent self-administered questionnaire forms to them by post, requesting them to answer the questions on the forms. Responses were collected from 3,252 non-smoking men, 3,296 non-smoking women and 2,111 smoking men, and subjected to analysis. Eighteen percent of non-smoking men were identified as having some form of metabolic syndrome symptoms and having access to “positive support” (through consultation provided by doctors, national registered dietitians, public health nurses, etc. on a continuous basis) to alleviate their conditions, while non-smoking women who measured 80 cm or more around the waist and who were identified as having access to “positive support” to alleviate their metabolic syndrome symptoms accounted for 10%. The total respondents were classified into quartiles, according to their volumes of milk and dairy product consumption. When the ratio of metabolic syndrome sufferers in the group consuming the lowest amount of milk and dairy products was regarded as 1, the ratios in the other three groups were significantly lower among non-smoking women as they consumed more milk and dairy products, while non-smoking men showed a similar trend. Our findings indicate that milk and dairy product consumption may be useful for prevention of metabolic syndrome in non-smokers.

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The present study examined the influence of shiftwork on lifestyle and diet in female nurses and caregivers. The subjects were 134 female nurses and caregivers aged 20-63 years, who completed a self-administered questionnaire pertaining to lifestyle and dietary habits. We found that shift workers consumed more sweet beverages and snacks than day workers. In addition, shift workers reported irregular lifestyles between shifts. The number of shift workers who missed breakfast or lunch was higher on days at the start and end of night shift than on days during the day shift. Moreover, in shift workers, we identified a significant and positive correlation between the number of years engaged in shiftwork and body mass index.

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